Although its implementation is likely to vary across states due to the recent Supreme Court decision, passage of the Affordable Care Act (ACA) is expected to dramatically impact the delivery of substance use disorder (SUD) treatment through changes to treatment financing and greater integration of mainstream health care and SUD treatment. The evolving system of buprenorphine treatment for opioid use disorders (OUDs) is a prime example of integration. While this system has grown substantially in the past decade, research is limited regarding how physicians are implementing this lifesaving treatment and whether they are delivering HIVrelated services. It is unknown how the ACA will impact the delivery of buprenorphine treatment. The proposed study seeks 1 year of R21 support to establish study feasibility and 4 years of R33 support to conduct a longitudinal study of buprenorphine implementation that integrates multi-level data on state-level variations in ACA implementation with longitudinal surveys of buprenorphine-prescribing physicians. The primary aim of the R21 phase is to determine the feasibility of conducting a longitudinal study that integrates physician-level and state-level data collection, through research procedures linked to 4 milestones encompassing the construction of the physician sample, survey development through qualitative and cognitive interviews, and generation of a protocol for longitudinal collection of state-level data on ACA implementation. The three specific aims of the proposed R33 study are: (1) To estimate cross-sectional and longitudinal models of buprenorphine utilization as well as the implementation of high-quality clinical practice behaviors (CPBs) and HIV-related services in buprenorphine treatment in the context of states implementation of the ACA; (2) To examine the relative importance of patient payment source (e.g., Medicaid, private insurance, or out-of-pocket) and other patient characteristics on physician decision-making during buprenorphine treatment; and (3) To model the state-level associations between the implementation of the ACA and two state-level outcomes: utilization of buprenorphine within Medicaid and the number of physicians holding the X-license for prescribing buprenorphine. These aims will be accomplished through ongoing collection of policy and administrative data at the state-level with 4 annual surveys of a nationally representative sample of 1,200 physicians who hold the X-license to prescribe buprenorphine. This longitudinal survey design will support fielding four unique conjoint analyses, each addressing a key domain of physician decision-making, while also collecting data on CPBs over time. Data analysis will include cross-sectional multivariate models of decision-making and multi-level longitudinal analyses of CPB adoption and implementation to test theory-driven hypotheses. By measuring the quality, availability, and utilization of buprenorphine treatment in the US, this research may identify treatment gaps for which interventions may be developed to improve treatment quality for OUDs while contributing to scientific knowledge regarding the impact of the ACA on US treatment services.